1. Field of the Invention
The invention pertains to strip-casting machine for producing a metal strip with two casting rolls set up next to each other to form a casting gap and with lateral sealing elements, each of which comprises a sealing plate which can be pressed against the end surfaces of the casting rolls on one side, where the sealing plate in question can be pressed against the two end surfaces of the casting roll in such a way that very precise contact can be achieved between the plate and the end surfaces of the casting rolls at the high temperatures of the casting operation.
2. Description of the Related Art
In a strip-casting machine of the general type in question according to EP-A 0,714,716, the device for sealing off the sides of the casting rolls consists of refractory sealing plates, one of which is pressed against the end surfaces of the two casting rolls on each side; these sealing plates prevent the molten steel poured in between the casting rolls from escaping toward the side. A metal bath is formed instead, as in a conventional mold. As these sealing plates are pressed against the rotating casting rolls, they are subjected to wear, which is accompanied by the large thermal load caused by the metal bath. The sealing plates are connected to a pressing device, which is designed in such a way that a disadvantageous wear pattern is necessarily formed on the sealing plates. One of the main problems of strip-casting machines of this type therefore remains unsolved, namely, the problem of ensuring that the lateral sealing elements offers a reliable seal throughout the entire duration of the casting operation.
In the case of casting rolls with small diameters in the range of approximately 500-800 mm, the seals to be provided for the roll sides are proportionately smaller. Because of the small volume of the metal bath, however, the surface of the molten bath is unsteady. In the case of large casting rolls with diameters of, for example, approximately 1,500 mm, the surface of the molten bath is calmer because of its larger volume. Although this is advantageous, larger and more complicated lateral sealing elements become necessary. As a result of manufacturing and installation tolerances, irregular wear, and differences in the degrees to which casting rolls are heated as a result of deposits, it is possible that the sealing edges or sealing surfaces of the rolls are not precisely aligned with each other.
From Japanese Patent Early Disclosure JP 4 [1992]-224,052 A, a strip-casting machine with two casting rolls is known, in which the frictional forces between a sealing plate and the end surfaces of the casting rolls are measured, and the pressing forces acting on the sealing plates are modified accordingly. This goal is to reduce asymmetrical wear on the sealing plate and to avoid the danger of the leakage of molten metal. The pressing forces are transmitted to the sealing plate by three hydraulic cylinders. The sealing plate is guided rigidly in an axial direction in a guide sleeve, which is disadvantageous.
In the document EP 0,806,997, a twin-roll casting system is described. The sealing plate for the two casting rolls consists of an upper and a lower part. The lower part of the sealing plate is pressed with much higher pressure against the end surfaces of the two casting rolls where they form the edges of the triangular gap than the upper part is. The upper sealing plate part is pressed by three cylinders against the rolls. The pressure applied by the cylinders is distributed uniformly over all the cylinders. The wear pattern of the sealing plate is necessarily irregular, even when a so-called xe2x80x9cspring returnxe2x80x9d for the individual pressure cylinders is provided as a restoring force. The danger of leakage as a result of premature wear of the sealing plates remains high.
The document EP 0,692,330 B1 deals with the casting of strip between two casting rolls, the end surfaces of which are sealed off by sealing walls. For the continuous determination of the state of the contact between the end surfaces of the rolls and the sealing walls, the frictional conditions are measured and compared with specified settings. At least one casting parameter is controlled on the basis of the results of the comparison. The position of the sealing wall can also be controlled on the basis of the value of the friction conditions. For this purpose, the sealing wall is held by an arrangement which consists of a main slide, which can slide in the direction of the rolls, and a secondary slide, which is guided horizontally on the main slide. Thus the sealing wall can be adjusted in two planes in order to measure the pressure or the forces on the sealing wall in the vertical and horizontal directions. The measurement setup does not, however, eliminate the danger of leaks at the sealing walls as a result of irregular wear.
A twin-roll continuous casting machine with side walls pressed against the rolls for the continuous casting of thin metal strips is also described in another document, namely, EP 0,698,433 B1. The side walls are connected to a pressure plate and a support plate, so that the side walls can be moved in the axial direction of the casting rolls and also perpendicular to that direction. Between the pressure plate and the support plate, several compression springs are inserted, which act on the side walls. Each side wall is surrounded by a cooled ring. The pressure plate is carried by a cart, which can move in the axial direction. On the cart there is an adjusting cylinder, which acts on the pressure plate. The previously known design, however, is unable permanently to prevent irregular wear of the side walls and thus unable to guarantee the required absence of leakage between the casting rolls and the side walls over the course of several casting sequences.
Against this background, the present invention was based on the task of improving a strip-casting machine of the general type indicated above in such away that the required absence of leakage at the lateral sealing elements is ensured during the entire casting operation, even when casting rolls of optimum diameter are used. Another goal is that it should be possible with the improved machine to deliver the lateral sealing elements quickly and after replacement has been completed to carry out operations reliably with them.
The task is accomplished according to the invention in that each sealing plate is supported in a floating manner so that it can be set or pressed against the rolls with freedom to move in three dimensions. As a result, very precise contact can be achieved between the sealing plate and the end surfaces of the casting rolls even at the high temperatures of the casting operation, and the wear of the sealing plate is reduced to a minimum.
In a highly advantageous embodiment, each lateral sealing element is attached to a carrier element. This carrier element consists of the sealing plate, a support frame holding the sealing plate, the setting or pressing means acting on the frame, and the floating support of these components on the carrier element.
In a further elaboration of the invention, it is provided that at least one of the casting rolls can be adjusted, especially in the axial direction, so that the end surfaces of the rolls can be aligned with each other on a plane as accurately as possible and/or aligned with respect to the sealing plates.
With this strip-casting machine according to the invention, optimum lateral sealing of the casting rolls is achieved, the functionality of the seals remaining effective for the entire duration of the casting operation even in the case of casting rolls with diameters of more than 1 meter.